This application is the US national phase of PCT application PCT/EP00/08115 filed Aug. 19, 2000 with a claim to the priority of German patent application 19955147.2 itself filed Nov. 17, 1999.
The present invention relates to a dryer having devices for blowing in a drying medium, conveyors arranged in levels and each formed as a roller conveyor, a drive system comprised of a plurality of endless chains each associated with at least one drive and a tensioning device.
Such a dryer is used for drying plate-like goods, in particular gypsum panels (see German patent document 4,326,877). It has several transport systems with vertically superposed roller conveyors, preferably in 6 to 14 levels. The rollers or each roller conveyor are driven by a motor and an endless chain. The chain can also be set up so that two roller conveyors are driven by one chain and its motor. The motor is at one end of the dryer while the opposite end is provided with a reversing and tensioning device for the chain.
The material is fed by an input device to the various levels, the dryer holding a number of panels closely juxtaposed and filling the usable width. The material is thus transported longitudinally along the conveyor through the dryer. Meanwhile a drying medium is directed at the upper surfaces of the panels.
A dryer is formed as a closed box with several sections. The number of sections is determined by the amount of drying and can be between 5 and 80. The capacity of the dryer is mainly limited by the tension that can be exerted by the belts the length of the dryer. The chain cannot be made of any possible strength, because the chain weight itself limits the chain tension. In addition a heavy-duty chain takes up substantial room and is expensive. Standard chains cannot be used beyond a certain dryer length.
Another system is known wherein for each pair of roller conveyors there are two drives. The chain is thus subdivided in the middle of the conveyor, that is instead of one chain for one conveyor or pair of conveyors, each chain having a drive that is arranged in the middle of the dryer and that has its own tensioning device. This system has the disadvantage that the drive system is expensive because it is necessary to duplicate the equipment. Furthermore sealing around the centrally mounted arrangement of the drives is difficult.
It is an object of the invention to make a dryer of the described type that has a large capacity and wherein a drive system of simple construction is used and where the drive is not exposed to high temperatures and the system is easy to seal.
The object is achieved in that each chain is connected to two drives of which one is at an output end and the other is at an input end. Since for each chain there is at both the input end and output end of the dryer a respective drive, the maximum tension that the chain is subjected to is roughly halved. In this manner either the chain can be made lighter or with the same chain the dryer length and capacity can be increased without having to make a more expensive drive system. The drives and tensioning systems can be arranged outside upstream and downstream ends of the dryer so that sealing is not a problem and they are only exposed to the surrounding environmental temperature.
Driving two roller conveyors with a single chain decreases the construction costs.
The location of a tensioning device in a reversing roller ensures free movability in the longitudinal direction with solid assuming of all applied forces.
Since two roller units are set parallel to each other, the individual units can be made smaller which has a particularly positive effect on the overall construction height.
The pendent mounting of the tensioning device reduces fouling and servicing.